Approach to skin nodules + nodular dermatitis Flashcards
What is a nodule?
*Circumscribed solid elevation greater than 1cm in diameter that usually extends into deeper layers of the skin
What causes formation of nodules?
Usually infiltration of
-inflammatory cells
-neoplastic cells
-deposition of fibrin / crystals (e.g. calcinosis cutis)
What are the 3 broad categories of infectious differentials?
*Bacteria
*Fungal / yeast / algae
*Protozoa / parasites
What are the bacterial differentials?
*Furunculosis
*Mycobacteria, Nocardia, Actinmyces
*Bartonella
What are some fungal / yeast / algae differentials?
*Cryptococcus, sporothrix
*Blastomyces, Histoplasma
*Dermatophytic pseudomycetoma
What are protozoal / parasitic differentials?
*Leishmania
*Neospora / Toxoplasma
*Dirofilaria
What are non infectious differentials?
- Foreign body (plant/Inorganic material →calcinosis)
- Inflammatory (eosinophilic granuloma)
- Cutaneous drug eruption, injection reaction
- Sterile pyogranulomatous dermatitis and panniculitis (Sterile nodular panniculitis)
- Juvenile cellulitis
- Histiocytosis
Considering clinical presentation what should be assessed?
*Location on body
*Number
*Size
*Ulcerated?
*Pigmentation
*Alopecic?
*Painful / hard / soft / movable / fixed / warm
How would you take a cytology of a nodule?
*Fine needle aspirate
*Apposition
How would you take a histology with a nodule?
1.Excision of whole nodule
or
2. Punch / wedge biopsy
*Freeze tissue for culture or PCR
What are further diagnostic tests that could be done?
*Immunohistochemistry
*Special stains
*PCR
*Biochemistry
*Serology
What are foreign bodies that could form nodules?
*Plant material
*Grass awns
*Embedded insect mouth parts
*Suture material
*Porcupine quills
What are endogenous material that could form nodules?
*Hair, sebum, keratin
*Calcium salt
*Tyrosine crystals
What is likely to cause infection from a dog bite?
Staphylococcus
What is likely to cause infection / nodule with cat bite?
*Fusobacterium
*Pasteurella
*Staphylococcus
*Streptococcus
What are the clinical signs of filamentous bacteria causing nodules?
- Nodules and abscesses, with ulcers, draining tracts and cellulitis →anywhere the bacteria are inoculated (mainly extremities, head and neck, and inguinal area) from bite wounds or penetrating foreign bodies
- Serosanguineous exudate
- Possible systemic signs – pyrexia, depression. With Nocardia occasional systemic dissemination and pneumonia
How is aetiological cause of a nodule diagnosed?
- Cytology +/- special stains (Gram, ZN) – filamentous bacteria might be seen
- Histology +/- special stains - nodular to diffuse pyogranulomatous dermatitis and panniculitis, with or without tissue grains “sulfur granules”
- Culture – can take weeks
- Molecular techniques (PCR, gene sequencing, MALDI-TOF)
How are filamentous bacteria nodules treated?
*Surgical drainage
*Antimicrobial therapy
What are filamentous bacteria that can cause nodules?
- Actinomyces – oral/GI tract, commensal
- Nocardia - cosmopolitan, soil saprophyte
- Actinobacillus - commensal organism in oral cavity
What are the clinical signs of a saprophytic mycobacteria nodule?
- single or multiple, firm, well‐circumscribed nodules in the skin or subcutis
- peripheral lymphadenomegaly
- Canine leproid granuloma (CLG) usually self-limiting
- Feline leprosy syndromes (FLS) progressive and occasionally aggressive clinical course
What can saprophytic mycobacteria nodules form in cats and dogs?
*Cats = Feline leprosy syndromes
*Dogs = Canine leproid granuloma
How is CLG treated?
Spontaneous regression in 1-3 months
How is FLS treated?
*Combination of 2/3 antibiotics,
*surgical excision
What are the clinical signs of a non-tuberculous mycobacteria nodule?
*Granulomatous panniculitis - Single/multiple nodules, plaques, macules and diffuse swelling –
multiple punctate ulcers and draining tracts (++ inguinal fat pad, tail base, flank)
* (Pyogranulomatous lobular pneumonia)
* (Disseminated systemic disease)
What are the clinical signs of M. tuberculosis nodules?
*Firm nodules, ulcerations, non-healing wounds with draining tracts →thick yellow to
green fluid + systemic signs
*+/- local or generalized lymphadenopathy
What pets are predisposed to M. tuberculosis?
Male outdoor cats
What is the treatment of M. tuberculosis?
*NOTIFIABLE DISEASE - owner might need TB screening
*Euthanasia / multidrug regimens
What cats are predisposed to dermatophytic pseudomycetoma?
Persian
DLH
How is dermatophyte nodules treated?
Systemic antifungals - intraconazole
What is the fungal cause of dermatophyte nodules in cats?
Microsporum canis
What are mycetomas?
*pyogranulomatous nodules that contain tissue grains or granules composed of dense colonies of organisms and necrotic debris
* Pigmented fungi
* Unpigmented fungi
What is chromomycosis?
*subcutaneous and systemic disease associated with pigmented fungal elements
* pigmented hyphal elements but NOT grains in tissues
What is Cryptococcosis?
- In the environment (soil, trees, bird droppings)
- Most common systemic mycosis in cats
How are subcutaneous fungal nodules treated?
*Azoles - systemic antifungals -itraconzaloe
*Amphotericin B
*Terbinafine
What mainly only causes nodular skin lesions in immune compromised patients?
Protozoa - toxo, neospora, leishmania
What are some immune mediated causes of nodules?
*Sterile pyogranulomatous dermatitis + panniculitis
*Eosinophilic granuloma
What are histiocytes?
overarching term to describe cells of dendritic cell (DC) or macrophage lineage
Are histiocytomas a concern?
No - solitary lesion that regresses in a few weeks
How are histiocytic proliferative disorders treated?
*Glucocorticoids
*Ciclosporin
